The invention relates to a thermoplastic film which is peelable and sealable. More specifically, the invention relates to a thermoplastic film with intermediate separable layers sandwiched between a core layer and a sealing layer which permits peeling of the core layer from the seal layer. The film also provides improved optical clarity.
A peelable film structure is described in WO 96/04178 published on Feb. 15, 1996. The film structure comprises a core layer comprising an olefin polymer and a heat sealing layer comprising a blend of low density polyethylene (LDPE) and a material incompatible with the LDPE, such as an olefin polymer or co- or terpolymer of ethylene, propylene or butene. The film structure can be heat sealed to a plastic container to form the lid of the container, or to itself to form a package. It is disclosed that when used with a plastic container, the film structure can be readily peeled from the container in order to open it.
In U.S. Pat. No. 5,358,792 a heat sealable composition is described comprising (a) from about 30 to about 70 weight percent of a low melting polymer comprising a very low density ethylene based copolymer defined by a density in the range of about 0.88 g/cm3 to about 0.915 g/cm3, a melt index in the range of about 1.5 dg/min to about 7.5 dg/min, a molecular weight distribution (Mw/Mn) no greater than about 3.5 and (b) from about 70 to about 30 weight percent of a propylene based polymer. U.S. Pat. No. 5,358,792 is incorporated herein by reference in its entirety.
U.S. Pat. No. 6,231,975, issued May 15, 2001, discloses an oriented sealable film comprising: (a) a core layer comprising an olefin polymer which comprises polypropylene, high density polyethylene or ethylene-propylene copolymer or terpolymer, wherein the polypropylene comprises greater than about 80 wt % of isotactic polypropylene or greater than about 80 wt % of syndiotactic polypropylene, wherein the percentages are based on the entire weight of the polypropylene of the core layer; (b) a sealing layer selected from the group consisting of ethylene-propylene random copolymer, ethylene-butene-1 copolymer, ethylene-propylene-butene-1 terpolymer, propylene-butene copolymer, low density polyethylene, linear low density polyethylene, very low density polyethylene, metallocene catalyzed polyethylene plastomer, metallocene catalyzed polyethylene, metallocene catalyzed ethylene-hexene copolymer, metallocene catalyzed ethylene-butene copolymer, metallocene catalyzed ethylene-octene copolymer, ethylene-methacrylate copolymer, ethylene-vinyl acetate copolymer and ionomer resin; and (c) a separable layer positioned between the core layer and the sealing layer, the separable layer comprising a blend of linear low density polyethylene and ethylene-propylene block copolymer.
This invention relates to a sealable film comprising:
(a) a core layer comprising an olefin polymer wherein the core layer comprises the interior of the film;
(b) a separable layer exterior to the core layer, wherein the separable layer comprises (1) an impact copolymer layer; (2) a thermoplastic polyolefin (TPO) layer; (3) a blend of impact copolymer and LLDPE; or (4) a blend of two or more incompatible polymers;
(c) an optic improving layer exterior to the core layer and the separable layer, wherein the optic improving layer comprises a polymer having an optic improving level of modulus, hardness, and/or beam strength; and
(d) a sealing layer exterior to the core layer, the separable layer, and the optic improving layer, wherein the sealing layer comprises a polymer.
Objects and advantages of the invention include one or more of the following:
To provide a thermoplastic film having at least four layers, including a seal layer, which is sealable to itself and other surfaces, but which permits separation of the seal layer from at least one other layer of the film.
To provide a thermoplastic film having one or more separable layers positioned to permit separation of the sealing layer from at least one other layer of the film.
To provide a multilayer film comprising a core layer and a sealing layer, so that when sealed to itself, or another surface, the sealing layer can be separated from the other layers of the film.
To provide a thermoplastic film suited for packaging applications.